Because air purity standards limit emissions of organic compounds into the atmosphere, paint manufacturers have been substituting water for organic solvents and diluents in their products. This trend poses a serious threat to existing markets for aluminum pigments, which are used extensively in organic-based coatings such as decorative automotive top coats, asphaltic roof coatings and metallic maintenance paints. Aluminum readily reacts chemically with water to produce hydrogen gas and aluminum hydroxide according to the chemical equation: EQU 2Al+6H.sub.2 O.fwdarw.2Al(OH).sub.3 +3H.sub.2
This reaction occurs relatively rapidly with aluminum pigments due to the high surface to mass ratio of the small particles, and the reaction destroys the unique metallic pigmentation properties of the tiny aluminum mirror-like particles by converting them to a hydrated oxide form unsuitable for pigment use. More importantly, the reaction also generates hydrogen gas, which is a fire and explosion hazard.
To a lesser degree, this same aluminum-water reaction also affects other particulate aluminum products used industrially as chemical intermediates, and in such products as rocket propellants, explosives, cold solders, structural adhesives and many other products. Accidental exposure to water, particularly during shipping or storage, poses the same safety hazards through hydrogen generation and the same potential functional losses through oxidation of the metallic aluminum.